still doesn't like to idle

[strohlde]

You can refer to other threads for my pains. It'll run great at non idle speeds but still chokes and stalls at idle (sometimes...not all the time). What else could it be? It's got a new IAC, fuel pump, MEFI.

MP 350 5.7

thanks

[boatwakes]

The last two sensors in the system are the air temp sensor and the coolant temp sensor. Both control idle fuel mixture ratio by giving temp info to the computer which then interprets and calculates fuel delivery. If the exhaust has a strong smell to it and the soot levels are visible on the transom and in the air, it's probably one or both of those sensors. It is also possible for either sensor to be out of spec without setting a code. For example, if the coolant temp sensor is reading at 65 degrees when the engine is really at 165, it is still within its parameters for the computer to program fuel delivery at that 65 temp. In this case, the computer will overfuel the engine at idle in order to speed up warm up time, thus excessive fuel in the exhaust and tangible soot. Good luck and keep us posted.

[strohlde]

I've not noticed any soot. Would the air temp sensor be the same temp I'm seeing on my dash? If so that seems to be about right. Also... would the coolant temp be the engine temp at the dash? If so that seems about right as well.

[strohlde]

Also.. I've tracked down the coolant temp sensor. Is there an air temp sensor on the marine power? I can't seem to find one in the parts manual.

[chpthril]

I've not noticed any soot. Would the air temp sensor be the same temp I'm seeing on my dash? If so that seems to be about right. Also... would the coolant temp be the engine temp at the dash? If so that seems about right as well.

No, the ECM typically has a dedicated sensor for the engine temp that is separate from the engine temp sender used for the gauge. The Air temp would also be a dedicated temp sensor that would read the engine compartment temp.

My feeling is that the boat was taken out of service, either for winter storage or to be sold, quite a bit ago and the fuel was not treated. it has since spoiled and crystallized in the injectors and or fuel rail. Being that you changed the fuel out in the tank and have since noticed a huge improvement, I would stay on the trail of spoiled fuel as the root cause. I would see about getting the injectors flow tested. If you know someone that works in a GM shop, you might see if they would loan you the old GM injector test tool. Probably collecting dust as it's all done through the scan tool nowadays, but still a good tool and will tell you alot.